1. Field of Use
This invention relates generally to carrier frames for vehicles. In particular, it relates to a carrier frame for a vehicle, such as a mobile crane or the like, which has apparatus such as a crane upper mounted thereon and which is supported during use by outriggers.
2. Description of the Prior Art
The prior art discloses various types of carrier frames for vehicles and the state of the art is disclosed in U.S. Pat. Nos. 3,945,666; 3,902,734; 3,759,540; 3,622,171; 3,528,678; 3,392,988; and 3,319,975. In particular, U.S. Pat. No. 3,622,171 discloses a vehicle frame for a mobile crane formed of longitudinally extending plates which define a hollow frame of inverted U-shaped cross section and having lateral re-enforcements spaced longitudinally along the frame. As the size and weight of mobile cranes and the loads to be handled thereby increase, it is necessary that the carrier frames be made stronger and more deflection resistant. On the other hand, the larger carrier frames must not become unduly heavy or unduly difficult and costly to construct.
Carrier frames of the mobile type that are subjected to heavy axial and overturning moments imposed by the turntable bearing for the crane mounted thereon have required strong heavy side sill or frame members to take the bending and torsional loads. These side sills have been of various types, including: two laterally spaced apart vertical channels connected by a horizontal top plate; two laterally spaced apart vertical wide-flange beams connected by a horizontal top plate; or two laterally spaced apart hollow parallel-sided fabricated boxes, the horizontal top plate of which may be integral with the two boxes. The aforementioned channel and wide flange beam sills are not balanced sections and have limited torsional strength. The aforementioned type using two hollow parallel-sided boxes with an integral top plate is a considerably more effective section, because it allows freedom to change the thickness or strength of each individual plate in order to suit a particular design. The shortcoming of the last-mentioned type, however, is that the top plate becomes needlessly heavy because of the large span between the two boxes forming the side sills and, in order to obtain a sufficiently strong top plate, the top plate has to be relatively thick.